|
03/10/2014:
I think it’s best to just wait till next dark cycle before logging Pal 3. I broke my own rule by reporting something based on only one night’s viewing instead of three.
The thread raises an idea I’ve toyed with over the years. Planetary and lunar lovers will look for hours awaiting that one second or so of perfect seeing that reveals Jupiter’s mid-belt festoons or see Rima Birt resolve into craterlets on the Moon. Atmospheric optics go from the glass equivalent of 1/4wave to 1/8 wave for a moment and then Pfft, back to ho-hum. I wonder if the same doesn’t apply to limiting magnitude. I know I see to mag 15.5 in the 180mm and 200mm scopes because I’ve got a seasonal set of standard objects that I clipped from WikiSky and annotated the star magnitudes down to 16.5. M67 is this season’s. If it’s a really good night I’ll look at M67 awhile to determine the faintest star I can see. To gauge seeing I use doubles from 0.7” to 2.0” in the Trumpler clusters in the Carina Neb. The Pal 3 session was a mag 15.1 night, and seeing was around 1.1 arcsec.
I wonder if the moments of near-perfect clarity that planetary folks get frostbite over also work for transparency. A moment comes along when the atmospheric lenses turn briefly into a big flat with no aberration, putting sub-arcsec faintnesses into the Airy disc instead of the rings. I certainly have seen plenty of objects much fainter than the rule books allow. I like globulars so much because they can resolves into at-the-limit spangles of glory as splendid as 47 Tuc. The same happens with the mag 14 galaxies in the Centaurus cluster. During this last session I logged the very reddened (12.9 mag!!) Westerlund I cluster in Ara, three separate times a night across three nights. If ever an object required patience and perfect skies, it’s that one. (Look it up on WikiSky if you want to see what reddening can do.)
Purry as I am over Robert’s esteem for my eyes, they are still 70 years old. Dark adaptation takes an hour and a half instead of ten minutes. Oh youth, youth, where art Thou?
=Dana
|